The present invention relates to a heating furnace tube, a method of using the heating furnace tube, and a method of manufacturing the heating furnace tube, and more particularly to a heating furnace tube whose problems are coking and carburization during operation at high temperature, such as a cracking tube of an ethylene plant, a method of using such a heating furnace tube and a method of manufacturing such a heating furnace tube.
In a cracking tube of an ethylene plant used as a heating furnace tube, for example, the coking is a problem, where carbon precipitates and deposits on the inner surface of the tube in the atmosphere of gas including carbon, such as, hydrocarbon, when the temperature is in the temperature range where carbon precipitation occurs.
If coking is generated on the inner surface of the heating furnace tube, such serious problems as overheating and plugging may occur during the operation of the plant. Therefore decoking to remove deposited carbon by burning in a high temperature steam atmosphere must be performed frequently, and to perform decoking, operation of the plant must temporarily be stopped, which causes a considerable drop in productivity.
Technologies which have been developed to solve this problem include the construction of a heating furnace tube made of material with Al-contained oxide film on the surface created by adding 1-10% Al to ferric alloy, or material with a high Al-contained layer created by aluminizing the surface of base alloy.
In these conventional art, however, coking resistance is actually improved, but it is not yet sufficient to use the tube as a heating furnace tube in an actual industrial furnace.
With the foregoing in view, it is an object of the present invention to provide a heating furnace tube which has good coking resistance and can prevent a drop in productivity due to decoking and a method of using the heating furnace tube.
In the case of a heating furnace tube which causes carburization, such as the case of a cracking tube of an ethylene plant, the depth of carburization on the inner surface of the heating furnace tube is measured regularly to prevent damage on the heating furnace tube caused by carburization, and since operation of the plant must be stopped at each measurement, productivity drops considerably.
Oxide dispersion strengthened (ODS) ferrous alloy, which is ferritic high chrome alloy (20Crxe2x80x945Alxe2x80x94Fe) where rare earth oxide is dispersed, is known to have an extremely excellent high temperature strength and carburization resistance compared with conventional materials, and is therefore applied to a heating furnace tube, including joining method using fusion welding, friction welding, blazing or mechanical joint method.
With the fusion welding method by TIG welding and electronic beam welding, which involves the fusion of joint areas, however, oxide particles float up and the dispersion strengthening function, which is a feature of rare earth ODS ferrous alloy, is lost, dropping high temperature to half or less.
With the friction welding method, which does not involve the fusion of material, high temperature strength does not drop very much but the high jointing pressure generates a big burr at the joint area of the heating furnace tube, which will block the flow of fluid in the heating furnace tube.
With brazing, high heat resistance cannot be expected because the melting point of the brazing filler metal is much lower than that of the base material, and with the mechanical joint method, such as riveting and screwing, maintaining air tightness at high temperature is extremely difficult, therefore both methods are inappropriate for jointing the heating furnace tubes.
In this way, conventional jointing methods have difficulties to meet requirements for the joint areas of heating furnace tubes, including carburization, air tightness and high reliability, in addition to extremely high temperature strength and carburization resistance.
With the foregoing in view, it is an object of the present invention to provide a heating furnace tube which can prevent a drop in productivity caused by carburization measurement as much as possible, and a method of manufacturing the heating furnace tube.
As mentioned above, an object of the present invention is to provide a heating furnace tube that can solve problems that occur to a heating furnace tube used for fluid that contains carbon, such as hydrocarbon, a method of using the heating furnace tube, and a method of manufacturing the heating furnace tube.
In other words, an object of the present invention is to provide a heating furnace tube that can implement extremely good coking resistance and can prevent a drop in productivity due to decoking as much as possible, and a method of using the heating furnace tube, as well as to provide a heating furnace tube that can prevent a drop in productivity due to carburization measurement as much as possible, and a method of manufacturing the heating furnace tube.
A heating furnace tube used for the fluid containing hydrocarbon or carbon monoxide, is made of rare earth ODS ferrous alloy which contains 17-26% of Cr by weight and 2-6% of Al by weight.
With this configuration, rare earth ODS ferrous alloy which contains 17-26% of Cr by weight and 2-6% of Al by weight has extremely good coking resistance, therefore coking by the operation of an ethylene plant can be minimized and the interval of decoking can be extended much longer than a conventional cracking tube, and as a consequence, a drop in productivity due to decoking can be prevented.
The heating furnace tube can have a heating furnace tube element on one side made of rare earth ODS ferrous alloy which contains 17-26% of Cr by weight and 2-6% of Al by weight is joined with an heating furnace tube element on the other side made of the above mentioned rare earth ODS ferrous alloy or heat resistant alloy by diffusion bonding via insert metal.
With this configuration, at least one heating furnace tube element is made of rare earth ODS ferrous alloy which has good carburization resistance, therefore the interval of replacing a heating furnace tube can be extended longer than a conventional heating furnace tube when used for an ethylene plant, and as a consequence, cost for heating furnace tube replacement due to the progress of carburization can be decreased, and a drop in productivity can be prevented because the interval of shutdowns of plant due to carburization depth measurement is extended.
Also with this configuration, cost of the plant can be decreased considerably by using a heating furnace tube element made of heat resistant alloy for a part of a long heating furnace tube of an ethylene plant.
The heating furnace tube can be used for allowing fluid containing 100 ppm or less of S in atomic weight units to flow, and is used in a 550xc2x0 C.-1000xc2x0 C. temperature range.
With this configuration, the coking on rare earth ODS ferrous alloy and heating resistant alloy can be minimized, therefore the interval of decoking can be extended much longer than a conventional heating furnace tube, and as a consequence a drop in productivity due to decoking can be prevented.
The heating furnace tube can have a coupling short pipe to which the joint side edge of the heating furnace tube element on one side and the joint side edge of the heating furnace tube element on the other side are inserted, and the heating furnace tube element on one side and the heating furnace tube element on the other side are joined via the coupling short pipe by performing diffusion bonding in a state where the joint side edges of the heating furnace tube element on one side and the heating furnace tube element on the other side and the coupling short pipe are contact with pressure by a pressurization means via insert metal which is disposed between the joint side edges of the heating furnace tube element on one side and the heating furnace tube on the other side and the coupling short pipe.
With this configuration, the joint side edge of the heating furnace tube element on one side and the joint side edge of the heating furnace tube element on the other side are connected via the coupling short pipe, which makes centering of the heating furnace tube element on one side and the heating furnace tube element on the other side easier in the manufacturing process.
The heating furnace tube can comprise a tapered surface created by the outer surface of the coupling short pipe and a tightener which engages with the tapered surface and contacts the coupling short pipe in the radius direction.
With this configuration, the joint side edges of the heating furnace tube element on one side and the heating furnace tube element on the other side can surely be contact with pressure with the coupling short pipe with a simple structure.
The heating furnace tube may have an insert metal formed by plating.
With this configuration, insert metal can be simply and surely disposed between the joint side edges of the heating furnace tube element on one side and the heating furnace tube element on the other and the coupling short pipe.
The heating furnace tube may be used in a 550xc2x0 C.-1200xc2x0 C. temperature range.
With this configuration, brittle fractures caused by 475xc2x0 C. embrittlement can be prevented and sufficient carburization resistance can be implemented.
A method of using the heating furnace tube can be characterized in that fluid containing hydrocarbon or carbon monoxide flows through the heating furnace tube made of rare earth ODS ferrous alloy which contains 17-26% of Cr by weight and 2-6% of Al by weight.
With this structure, rare earth ODS ferrous alloy which contains 17-26% of Cr by weight and 2-6% of Al by weight has extremely good coking resistance, therefore coking by operation of an ethylene plant can be minimized and the interval of decoking can be extended much longer than a conventional cracking tube, and as a consequence a drop in productivity due to decoking can be prevented.
The heating furnace tube element on the other side can be made of heat resistant alloy that is joined via insert metal by diffusion bonding.
With this configuration, the heating furnace tube element made of heat resistant alloy is used for a part of a long heating furnace tube of an ethylene plant, which can decrease the cost of the plant considerably.
The heating furnace tube can allow fluid containing 100 ppm or less of S in atomic weight units to flow, and be used in a 550xc2x0 C.-1000xc2x0 C. temperature range.
With this configuration, coking on rare earth ODS ferrous alloy and heat resistant alloy can be minimized, therefore the interval of decoking can be extended much longer than a conventional heating furnace tube, and as a consequence a drop in productivity due to decoking can be prevented.
A method of manufacturing a heating furnace tube comprises joining a heating furnace tube element on one side made of rare earth ODS ferrous alloy which contains 17-26% of Cr by weight and 2-6% of Al by weight with the heating furnace tube element on the other side made of rare earth ODS ferrous alloy or heat resistant alloy by diffusion bonding via insert metal, characterized in that the manufacturing method comprises of a process for forming or inserting the insert metal to at least one of the joint side edge of the heating furnace tube element on one side and the joint side edge of the heating furnace tube element on the other side, a process for contacting with pressure the joint side edge of the heating furnace tube element on one side and the joint side edge of the heating furnace tube element on the other side directly or via intermediate member, and a process for performing diffusion bonding the heating furnace tube element on one side and the heating furnace tube element on the other side by heating the insert metal.
With this configuration, at least one heating furnace tube element is manufactured to be a heating furnace tube made of rare earth ODS ferrous alloy with good carburization resistance, therefore the interval of heating furnace replacement can be extended longer than a conventional heating furnace tube when used in an ethylene plant, and as a consequence a drop in productivity can be prevented.
The manufacturing method of a heating furnace tube can comprise the insert metal being formed by plating.
With this configuration, the insert metal can be simply and surely disposed between joint side edges of the heating furnace tube element on one side and the heating furnace tube element on the other side and the coupling short pipe.
The manufacturing method of a heating furnace tube can comprise the intermediate member being a coupling short pipe to which the joint side edge of the heating furnace tube element on one side and the joint side edge of the heating furnace tube element on the other side are inserted, and the heating furnace tube element on one side and the heating furnace tube element on the other side are joined via the coupling short pipe by performing diffusion bonding in a state where the joint side edges of the heating furnace tube element on one side and a heating furnace tube element on the other side and the coupling short pipe are contact with pressure by a pressurization means via the insert metal disposed between the joint side edges of the heating furnace tube element on one side and the heating furnace tube element on the other side and the coupling short pipe.
With this configuration, the joint side edge of the heating furnace tube element on one side and the joint side edge of the heating furnace tube element on the other side are joined via a coupling short pipe as an intermediate member, which makes centering of the heating furnace tube element on one side and the heating furnace tube element on the other side easier in the manufacturing process.
A manufacturing method of a heating furnace tube is characterized in that the pressurization means made of the tapered surface created on the outer surface of the coupling short pipe and a tightener which engages with the tapered surface and contacts the coupling short pipe in the radius direction.
With this configuration, the joint side edges of the heating furnace tube element on one side and the heating furnace tube element on the other side can be surely contact with pressure with the coupling short pipe with a simple structure.